1. Field of the Invention
This invention relates to television signal detecting circuits, and more particularly to a television signal detecting circuit which can prevent an erroneous operation caused by a noise and the like.
2. Description of the Prior Art
Heretofore, it has been the common practice to detect the presence or absence of the television signal for the purpose of controlling a vacant channel skip circuit or a sleep circuit. That is, television receivers capable of being remotely controlled have been arranged to scan through all of the channel frequencies in response to a control signal and to automatically skip each vacant channel on which no signal is being received and to select the next channel on which a signal is present. It has also been known to use means referred to as a sleep switch which is made conductive when a user goes to bed and which can automatically cut off an electric source when the television station goes off the air for the night.
Prior art television signal detecting circuits, which can only detect a video signal, synchronizing signal or the like, have the disadvantage that their signal detecting operation becomes unreliable when the electric signal is weak, such circuits are liable to respond to the noise signal as if it were a television signal.